Once the favorite breed of King Charles II of England, the small sporting spaniel was first dubbed the King Charles Spaniel. Then oriental breeds came into fashion and breeders began crossbreeding the spaniels to achieve a more snub-nosed, round-headed look. In 1926, a wealthy American visited England in search of the small spaniels so often seen in portraits of King Charles. But there were none. So he offered monetary prizes to be awarded at the famed Crufts Dog Show for the male and female most closely resembling the original King Charles Spaniel. British breeders rose to the occasion and by 1945, the recreated breed had arrived. To avoid confusion with the now-snub-nosed King Charles Spaniels, the breed was named the Cavalier King Charles Spaniel since Charles was known as the Cavalier King.

The Cavalier breed was developed by selective breeding of long-snouted King Charles Spaniels (also known as English Toy Spaniels). The development of the Cavalier King Charles Spaniel was partly due to a desire to produce a long-nosed toy spaniel, as are seen in the paintings of the great masters. Long-snouted toy spaniels no longer existed at the beginning of the 20th century, due to crosses between long-snouted toy spaniels and short-snouted breeds such as the Pug or Japanese Chin in the 18th-19th century.